AC to AC converters are known in the art for a variety of applications. Typically, an AC supply voltage is rectified and the DC voltage is converted to a variable frequency AC voltage by a converter. The switching action of the power switches in the converter bridge results in a certain amount of electromagnetic interference (EMI) propagating in the circuit. The amount of EMI appearing on the AC supply line must be limited in order to avoid adverse effects on other electrical apparatus.
The invention described in U.S. patent application Ser. No. 748,077, filed concurrently herewith and of common assignment, teaches that it is desirable to operate some types of arc discharge lamp from a full-bridge AC converter. When an arc lamp is operated on an AC voltage, the arc must be reignited during each reversal of lamp voltage. During the time that the arc is extinguished the lamp discharge medium deionizes slightly, thus raising the voltage which will reignite the arc. Therefore, the direction of the converter output should be switched when the voltage applied to the arc lamp will be at a maximum, which occurs when the DC voltage is at its maximum.
As demonstrated in U.S. patent application Ser. No. 562,919, filed Dec. 19, 1983, now U.S. Pat. No. 4,567,404 issued July 28, 1986, and assigned to General Electric Company, the high frequency voltage signals of a starting oscillator in a discharge lamp ballast may be restricted to the ballast by selectively inhibiting the oscillator when the diodes of the diode rectifier supplying DC power to the lamp are on.